Lightning damage

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This topic contains 5 replies, has 3 voices, and was last updated by  Rhapsode 4 years, 3 months ago.

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July 8, 2013 at 16:49 #6571

Rhapsode
Participant

To be honest I don’t think adding a trailing earth wire into the sea will make any difference for a full or partial strike. The inductance of the wire will probably present a higher impedance path than simply blasting through 15mm of hull. However it will reduce charge buildup for near strikes and ionisation effects so it will be a good thing to help protect electronics and occupants of the boat.

You could add an external earth plate close to the base of the mast and joined by a 3 inch, bend free, copper strap with a suitable bonding kit to prevent corrosion and electrolytic effects. It would certainly reduce damage in a strike but I’m not sure it is worth the effort.

Lightening is funny stuff, the current risetime is in the order of 8 microseconds and it will flash across a gap rather than go around a bend in the wire. I used to analyse radio tower grounding systems and the computation outputs used to surprise me sometimes. If you are really paranoid keep a spare radio and gps in a sealed tin box, they will then survive the electrical storm for later use to report the lightening damage in your holed boat.

By the way there is a lot of crap sold to protect installations and buildings, don’t touch early streamer or radioactive ionisation products, they are a complete waste of money. Use a good old Franklin rod and copper strap to a good earth rod (on land). It is just as good as anything else and costs a fraction of the high tech alternatives.

Andy

Ps,
I do know what I am talking about on this topic. Trust me, I’m an engineer :p

July 8, 2013 at 20:41 #13831

Orion
Participant

Orion sails Southern California and Baja waters. I haven’t seen lightning, in 20 years. However, I had a molded keel Pearson 24, when I was living off of Cape Cod. A neighbor’s boat, with a keel stepped mast, and grounding to a keel bolt, still had a square foot hole punched through his fiberglass hull, by a lightning strike. Apparently, the paint on the keel prevented grounding. So, I kept 10 feet of #2 braided copper cable, on a hook, at the base of my mast, and just threw it over the side, when there was any threat. Not elegant..but the locals claimed it was the only sure way. I’ve heard that splitting a cable, from the mast, to a couple of bronze thru-hull fittings, can help minimize the damage.

July 9, 2013 at 09:02 #13841

Rhapsode
Participant

I did wonder whether it would be sensible to fit a dedicated grounding plate akin to an SSB grounding plate – but on the other hand would a nicely grounded mast prove attractive to lightning bolts? Hard to know.

July 9, 2013 at 22:06 #13851

Orion
Participant

My experience, in W. Falmouth, a dogleg harbor, with tall trees around, and plenty of taller masts, was that lightning was unpredictable. It would bypass trees and tall aluminum masts, and hit what it hit, randomly. Lightning couldn’t seem to figure out the best conductor, and it hit in a physical way, like a sledgehammer..not electrically. It would physically blast a hole in a boat’s bottom..not melt or burn it. I’m not fully aware of how lightning damages electronics, through surges. But that wasn’t important if all the electronics was under 10 feet of salt water. I was aboard my boat, there, when hurricane Gloria hit Buzzards Bay. It was the only time I’ve ridden out a hurricane, aboard. That’s why I live in So. Cal., now.

July 10, 2013 at 10:13 #13861

Rhapsode
Participant

From your experience Orion the hook arrangement sounds best – divert the strike before it gets to the bottom of the boat!

July 27, 2013 at 16:15 #8401

Admin
Member

To be honest I don’t think adding a trailing earth wire into the sea will make any difference for a full or partial strike. The inductance of the wire will probably present a higher impedance path than simply blasting through 15mm of hull. However it will reduce charge buildup for near strikes and ionisation effects so it will be a good thing to help protect electronics and occupants of the boat.

You could add an external earth plate close to the base of the mast and joined by a 3 inch, bend free, copper strap with a suitable bonding kit to prevent corrosion and electrolytic effects. It would certainly reduce damage in a strike but I’m not sure it is worth the effort.

Lightening is funny stuff, the current risetime is in the order of 8 microseconds and it will flash across a gap rather than go around a bend in the wire. I used to analyse radio tower grounding systems and the computation outputs used to surprise me sometimes. If you are really paranoid keep a spare radio and gps in a sealed tin box, they will then survive the electrical storm for later use to report the lightening damage in your holed boat.

By the way there is a lot of crap sold to protect installations and buildings, don’t touch early streamer or radioactive ionisation products, they are a complete waste of money. Use a good old Franklin rod and copper strap to a good earth rod (on land). It is just as good as anything else and costs a fraction of the high tech alternatives.

Andy

Ps,
I do know what I am talking about on this topic. Trust me, I’m an engineer :p

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